Detecting low concentration levels of vapors in a particular atmosphere can be critical to the health of workers, the occupants of the eco-system, or the completion of an industrial or research process. Often times, a quick, sensitive and portable gas detector is needed. In many circumstances, a gas detector or detection system capable of detecting mixtures of vapors is required.
Although a variety of methods and devices for chemical gas sensing have been developed, including cantilever-based sensors and calorimetric-based sensors, the needs have not been fully met. The existing cantilever-based and calorimetric-based gas detectors are generally bulky and difficult to make them portable without sacrificing sensitivity. The existing capacitance-based gas detectors, though less bulky, are also low in sensitivity, especially with less expensive units. The existing capacitance detectors are generally derived from the conventional dielectric capacitors with polymers as the electrolytes. When the polymer is exposed to an organic vapor/analyte, the analyte becomes physisorbed in the polymer, which changes its dielectric coefficient, and in turn, alters the capacitance of the detector and signals the presence of an analyte. Polymer-based dielectric capacitors have been developed that are quite small (on the order of a few hundred microns) and which use inter-digitated electrodes separated by 1–2 μm with a polymer layer of approximately 5 μm. At this size, these capacitors generally exhibit nominal capacitance values in the picofarad range. Furthermore, since the capacitance variances are triggered by changes in the dielectric coefficient of a polymer upon absorption of volatile organic compounds, these variances are expected to be small and typically fall in the attofarad range. Consequently, the dielectric capacitance detectors require sophisticated, highly sensitive and expensive measuring devices to measure these small capacitance variances. In addition to the necessity for sophisticated measuring devices, the small capacitance variances can essentially impose a constraint on the detection limit of the device. Polymer-based capacitive sensors that have a detection limit of approximately 5 ppm for ethyl alcohol have been reported in the literature. The existing dielectric capacitance-based gas detectors further suffer from a slow analyte diffusion rate through the conductive polymer, which prolongs the chemical detection response and the recovery process.
Therefore, a need exists for a gas detector that can quickly and reliably detect a change in capacitance caused by an analyte contacting a sensing material, and further needed, is a gas detector or detection system that can detect the presence of and analyze the concentrations of multiple vapors in an environment, particularly hazardous vapors.